Inhibition of STAT3 signaling induces apoptosis and suppresses growth of lung cancer: good and bad

Abstract

Signal transducer and activator of transcription 3 (STAT3) modulates a variety of genes involved in the regulation of critical functions, including cell proliferation, differentiation, apoptosis, angiogenesis, metastasis, and immunity. For many cancers, elevated levels of STAT3 signaling have been associated with a poor prognosis and the development of chemotherapy resistance. In this study, we investigated the inhibitory effects of a novel small-molecule inhibitor of STAT3, STX-0119, on the cell viability and survival of human lung cancer cells. STX-0119 inhibited activated STAT3 and the expression of STAT3-regulated oncoproteins such as c-Myc, cyclin D1, and survivin in lung cancer cells. STX-0119 also decreased the amount of STAT3 in the nuclear fraction as well as induced apoptosis of these lung cancer cell lines as evidenced by increases in apoptotic cells (Annexin V positive) and poly (ADP-ribose) polymerase (PARP) cleavage. The efficacy of STX-0119 in a mouse xenograft model was confirmed. However, a hematological side effect, which had not been previously reported, was observed. The level of white blood cells was significantly lowered when treated at the dose at which STX-0119 alone showed a significant tumor-suppressive effect. In conclusion, we suggest that STX-0119 may be a potent therapeutic agent against lung cancer. Consideration of the side effect suggests, it is necessary to study whether low-dose STX-0119 is effective for lung treatment with a combination of classic lung cancer therapeutics.

Keywords: Cancer; NSCLC; STAT3 inhibitor; STX-0119; Xenograft.

Fig. 1

Suppression of STAT3 target-gene expressions by STX-0119 in lung cancer cells. a Effect of STX-0119 on Tyr705 phosphorylation of STAT3 in A549 cells. Cells were treated with indicated doses of STX-0119 for 48 h. b Subcellular localization of STAT3 in STX-0119-treated A549 cells. c Protein expressions of c-Myc, cyclin D1, and survivin in A549 cells after STX-0119 treatment for 48 h

Fig. 2

Inhibitory effect of STX-0119 on viability and survival of lung cancer cells. a Cell proliferation was measured after A549, H1299 and H23 cells were treated with the indicated concentrations of STX-0119 for 48 h. b Anchorage-dependent colony formation assays for cancer cells were performed following treatment with STX-0119 for 2 weeks. Representative pictures of colonies (upper panel) and quantitative analysis of colony numbers (bottom panel). Values presented are means ± SD. Statistical analysis was performed by applying Student’s t-test (*p < 0.05, **p < 0.005)

Fig. 3

Induction of apoptosis in lung cancer cells by STX-0119. a After incubation with STX-0119 for 48 h, H1299, A549, and H23 cells were stained with Annexin V and PI solutions. b A549, H1299, and H23 cells were treated with STX-0119 for 48 h, followed by western blot analyses of whole-cell lysates using an anti-PARP antibody that recognizes cleaved PARP

Fig. 4

Inhibitory effect of STX-0119 on tumor growth of A549 cells. a Athymic nude mice were xenografted with lung cancer cells and administered STX-0119 orally three times a week for 3 weeks. b Immunohistochemistry results for c-Myc, cyclin D1, and TUNEL in mouse tumor tissue as visualized by light microscope (× 200). Scale bar, 60 μm